The present invention relates to a sewing machine designed to perform stitches simultaneously on the opposite edges of a semifinished article, in particular a sewing machine of the type with a gap between the needles where the article of clothing or similar obJect is arranged during sewing.
It is known from previous studies by the same applicant to design sewing machines which have a gap in the middle and which are able to sew the opposite edges of numerous articles of clothing in a single sewing operation.
The operation of these sewing machines is not restricted by the need for the two edges to be sewn to be parallel with each other; in fact, as a result of a process perfected by the same applicant, mere tensioning of the articles of clothing can lead to substantial straightening of the edges during sewing.
However, a significant problem connected with the sewing machines mentioned above is how to adjust the distance between the needles, since, in some cases, the two lines of stitches must be very close to each other, while, in other cases, they must be separated by a distance which is sufficient to allow even bulky articles of clothing to be inserted in the gap provided between the sewing components. The problem arises from the fact that, on the one hand, the various sewing components must be properly connected to each other whereas, on the other hand, the working surface of the machine described must be divided into two separate support plates so that arrangement of the said gap is made possible.
The same applicant has already perfected a sewing machine in which two separate support plates form the base of a bridge-type structure which accommodates an internal shaft connecting together the various sewing components. This internal connection shaft is in practice provided with a sleeve coupling which allows axial extension of the shaft itself in accordance with the distance between the two needles and the associated lower sewing components.
Practical tests have demonstrated the validity of the solution proposed by the applicant. However, it also became apparent that the entire bridge-type frame of the sewing machine in question must be designed with a very high degree of precision so that when the operations necessary for moving the sewing components away from each other or towards each other are performed, the two sections of the said connection shaft remain perfectly aligned with respect to each other. Even in the case of very precise and hence costly design of the bearing frame of the said machine, in many cases jamming of the connected parts or at least binding of the connection mechanisms occurred, thus giving rise to a great deal of wear and high levels of power consumption.
Another typical problem of these sewing machines consists in the fact that the said machines have a relatively high purchase price which in many cases is disproportionate compared to the requirements of small users. The latter always have the possibility of performing all the sewing operations using individual machines, i.e. of the right-hand or left-hand type, and there is therefore the tendency to buy machines with a bridge structure only when, in practice, work requirements call for use of the same.
In doing so, a large number of users in many cases decide to do without the rapidity and operational features which characterize the sewing machines described above.